1. Field of the Invention
The present invention relates to an X-ray mask structure for use in the manufacture of semiconductor devices and the like, an X-ray exposing method by the use of the X-ray mask structure, a semiconductor device manufactured by the use of the X-ray mask structure, and a method for manufacturing the X-ray mask structure.
2. Related Background Art
In recent years, there has been a tendency that each line width of patterns on Integrated circuits is reduced as much as 70% in about three years time, with the increase of density and processing speed of the semiconductor integrated circuits. Due to the further integration of large capacity memory elements, further improvement in the performance of associated printing equipment is also required. Thus, this has begun to demand such a high performance that a transferable minimum line width is 0.3 .mu.m or less.
Therefore, a stepper utilizing light in an X-ray region (2 to 20 .ANG.) as exposure wavelength light is being developed. An X-ray mask structure for use in such X-ray exposing equipment has heretofore possessed such a constitution as shown in FIG. 19F formed by a manufacturing process elucidated in FIGS. 19A to 19F. In this structure, nothing is formed on the portion of an X-ray permeable film having no X-ray absorber pattern thereon.
In detail, reference numeral 21 is a substrate which will be a supporting frame, and as the substrate, an Si wafer is often used. As an X-ray permeable film 22, there is used a thin film having a thickness of about 2 .mu.m and comprising silicon nitride, silicon carbide or the like which is excellent in X-ray permeability.
A chromium film having a thickness of 50 .ANG. as a metal thin film 23 for gold adhesion and a gold film having a thickness of 500 .ANG. as a plating electrode 24 for the formation of an X-ray absorber are continuously deposited by EB vacuum deposition, as shown in FIG. 19A.
On the plating electrode 24, a desired fine resist pattern 25 is formed by means of an electron ray depictor, as shown in FIG. 19B. The resist to be used may have a single-layer form or a multi-layer form.
Next, gold is plated to form a gold film which will be an X-ray absorber 26. The resist pattern 25 is then peeled off, as shown in FIG. 19C.
The portion of the plating electrode 24 having no X-ray absorber 26 thereon is peeled off by etching with an argon gas. In this case, the plating electrode 24 and the X-ray absorber which are both made of gold are equally etched, so that the X-ray absorber takes such a form as represented by numeral 26' in FIG. 19D.
Afterward, the portion of the chromium thin film 23 having no X-ray absorber 26' thereon is peeled off by sputtering-etching with an argon gas or by etching with a reactive gas (a chlorine-based gas), as shown in FIG. 19E.
In the last step, the back of the Si wafer is etched to form the supporting frame 21, as shown in FIG. 19F.
In the conventional manufacturing process of the X-ray mask structure, the thickness reduction of the gold film is large and so the contrast of the X-ray mask structure is poor, because a sputtering ratio of chromium is lower as compared with that of gold, when the portion of the chromium thin film 23 having no X-ray absorber 26' thereon is peeled off by the sputtering-etching with the argon gas.
A difficulty in the manufacture process of the X-ray mask structure resides in that a fine pattern (on a level of 0.25 .mu.m) having a thickness of about 0.75 .mu.m and a high aspect ratio must be formed to obtain a desired contrast. It makes it more difficult to form a little thicker gold film in consideration of a film thickness quantity which is reduced at the time of the etching of chromium. Furthermore, in the case of the etching manner using the reactive gas, the chlorine-based gas is used, and therefore even if the uneven state of the etching is slight, silicon nitride or silicon carbide which is the X-ray permeable film is inconveniently etched, so that film thickness non-uniformity takes place and the film surface suffers damage. Even in the case of the sputtering-etching manner using the argon gas, the film thickness non-uniformity occurs and the film surface suffers damage.
Furthermore, when the metal thin film remains, this remaining film has little influence on the X-ray permeability but largely reduces alignment light permeability. In the case that the chromium film having a thickness of 50 .ANG. remains, the X-ray permeability deteriorates as slightly as 0.6%, but the alignment light permeability (with an He-Ne laser) lowers by as much as 46%.
Moreover, the X-ray absorber can be formed by etching W or Ta, but in this case, the reactive gases (mainly comprising fluorine) are used. Most of these gases have a high etching grade for silicon nitride or silicon carbide constituting the X-ray permeable film, so that the film thickness non-uniformity takes place and the film surface suffers damage. For the prevention of these troubles, a metal thin film for an etching stopper can be formed, and the film thickness non-uniformity and the damage can be inhibited as much as the thickness of the thin film, but nevertheless, similar problems are still present.